This application proposes to analyze the cytokine response to Cryptosporidium infection in immunocompetent human hosts and people with AIDS. These investigators hypothesize that differential intestinal cytokine production accounts for the symptoms (and resolution of symptoms) in immunocompetent hosts, and the development of chronic infection in people with AIDS. The investigators propose that Cryptosporidium infection in immunocompetent hosts may be divided into three broad phases: injury, control, and healing. The specific aims for this project include: 1) Identification and quantitation of mucosal cytokines during the injury phase of cryptosporidiosis in both normal volunteers and people with AIDS. 2) Identification and quantitation of mucosal cytokines during the control phase of cryptosporidiosis and correlation with oocyst excretion, CD4+ cell count, HIV viral load, stool volume, intestinal inflammation, and fecal anti-cryptosporidial IgA. 4) A trial of recombinant IL-12 as adjunctive therapy in chronic cryptosporidiosis in AIDS will be performed.